PMSG Wind Turbine Stability Analysis for Weak Grids With P&O Control
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Solution Overview
Problem
Traditional stability analysis methods for permanent magnet synchronous generator-based wind turbines connected to a weak power grid struggle with nonlinear discontinuous links, particularly when using the perturbation and observation method, as they ignore the power loop, leading to inaccurate results.
Innovation Solution
The method employs a describing function approach to model the power loop and analyze stability, considering nonlinear links, by establishing small-signal models and deriving a transfer function G(s) to assess system stability, including the influence of a weak AC power grid, and determining oscillation characteristics when the system is critically stable.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional small-signal stability analysis method is used, then the analysis process is simple, but it ignores the nonlinear power loop based on P&O method, leading to inaccurate stability analysis results
Solution Approach 1:
The patent introduces a describing function as an intermediary element to bridge the gap between traditional linear analysis methods and nonlinear system behavior. The describing function characterizes the nonlinear power loop by representing it as an equivalent gain that depends on the amplitude of the input signal, allowing the nonlinear system to be analyzed using linear frequency response methods while still accounting for nonlinear effects
Solution Approach 2:
The patent transforms the nonlinear power loop characteristics into a parameterized describing function N(A) where A represents the amplitude of the input signal. This parameter change approach allows the nonlinear system to be analyzed by varying the amplitude parameter and observing how the equivalent gain changes, thereby capturing nonlinear effects without requiring complex nonlinear analysis methods
2Ease of operation
If P&O method is used for maximum power point tracking, then no wind speed measurement is needed, but it introduces nonlinear discontinuous links that make traditional stability analysis difficult to apply
Solution Approach 1:
The describing function serves as a mediator that translates the discontinuous nonlinear P&O control logic into a continuous equivalent gain representation. By characterizing the switching behavior of the P&O method through its describing function, the patent enables the nonlinear control loop to be incorporated into stability analysis without requiring modification of the actual P&O controller
Solution Approach 2:
The patent replaces the need for direct nonlinear analysis of the P&O control logic with an equivalent linear frequency response analysis using the describing function. This substitution allows the complex nonlinear control behavior to be analyzed using simpler linear system tools, effectively replacing mechanical nonlinear analysis with electrical frequency domain analysis
3Reliability
If conventional stability analysis ignoring power loop is used, then the analysis is straightforward, but it fails to account for the influence of power control on system stability
Solution Approach 1:
The describing function acts as an intermediary that incorporates the power loop's influence into the stability analysis without requiring detailed modeling of the power loop's internal switching dynamics. The equivalent gain representation allows the power loop's stabilizing or destabilizing effect to be captured in a simplified manner
Solution Approach 2:
The patent applies partial action by focusing only on the essential characteristic of the power loop (its amplitude-dependent gain) rather than modeling all aspects of the power loop in detail. This partial modeling approach captures the critical stability-influencing behavior while avoiding excessive complexity from complete power loop modeling
Data Source
AI summary
Provided is a method for analyzing the stability of a PMSG-WT connected to a weak power grid considering the influence of power control. New energy power generation mostly uses a perturbation and observation (P&O) method for maximum power point tracking, and nonlinear discontinuous links therein make stability analysis difficult. The present application analyzes the stability of the PMSG-WT connected to the weak grid system based on a describing function method, and fully considers the nonlinear discontinuous links in the power loop, thus making the analysis result more accurate. At the same time, the describing function method is a method that can quantitatively calculate the frequency and amplitude of oscillation. The analysis method of the present application can provide a powerful and good reference for oscillation suppression and controller design.